Forming chemical vapor depositable low dielectric constant layers

ABSTRACT

Carborane may be used as a precursor to form low dielectric constant dielectrics. The carborane material may be modified to enable it to be deposited by chemical vapor deposition.

BACKGROUND

[0001] This invention relates generally to techniques for formingintegrated circuits.

[0002] In many integrated circuits, dielectric materials are utilizedbetween conductors such as metal lines. The dielectric constant of thedielectric materials determines the capacitance between those metallines. Generally the greater the capacitance the slower the operation ofthe lines. Slower operating speeds reduces performance of manyintegrated circuits.

[0003] Thus, it is desirable to provide dielectric constants ofdielectric materials that are as low as possible. In addition, it isdesirable that the dielectrics be deposited using chemical vapordeposition which is a well established process in the semiconductorindustry.

[0004] Thus, there is a need for ways to provide mechanically robust lowdielectric constant dielectric films that can be deposited by chemicalvapor deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a depiction of a carborane molecule or a fluorinatedcarborane molecule;

[0006]FIG. 2 is a depiction of a methyl or trifluoromethyl carboranemolecule;

[0007]FIG. 3 is a depiction of para-carborane;

[0008]FIG. 4 is a depiction of ortho-carborane;

[0009]FIG. 5 is a depiction of the synthesis of m-TEOS-carborane inaccordance with one embodiment of the present invention;

[0010]FIG. 6 is a depiction of ortho-triethylorthosilyl(TrEOS)-carborane in accordance with one embodiment of the presentinvention;

[0011]FIG. 7 is a depiction of meta-TrEOS-carborane in accordance withone embodiment of the present invention;

[0012]FIG. 8 is a depiction of para-TrEOS-carborane in accordance withone embodiment of the present invention;

[0013]FIG. 9 is a depiction of the synthesis of m-SiH₃-carborane inaccordance with one embodiment of the present invention;

[0014]FIG. 10 is a depiction of ortho-SiH₃-carborane in accordance withone embodiment of the present invention;

[0015]FIG. 11 is a depiction of para-SiH₃-carborane in accordance withone embodiment of the present invention;

[0016]FIG. 12 is a depiction of para-SiH₃-carborane in accordance withone embodiment of the present invention;

[0017]FIG. 13 is a depiction of synthesis of a three-dimensionalcarborane containing network in accordance with one embodiment of thepresent invention.

DETAILED DESCRIPTION

[0018] A mechanically robust, low dielectric constant film can be formedby chemical vapor deposition using carborane. Carborane, shown in FIGS.1 and 2, is a well known molecule precursor to high temperaturenon-oxide ceramics. The group R₁ may be hydrogen or fluorine, in FIG. 1,and CH₃ or CF₃ in FIG. 2. Carborane is a thermally stable cagedstructural molecule with a cage size of approximately 10 Angstroms or 1nanometer from vertex-to-vertex van der Waals diameter. Other materialshaving a pore size less than two nanometers may also be used.

[0019] Thus, the carborane cage size is sufficiently small to provide arelatively closed pore. By introducing the carborane, a dielectricconstant of a film can be reduced below 2.5 because the carborane is anon-polar organic moiety that possesses a low dielectric constant andbecause the cage structure of carborane reduces the density of the film,further reducing the dielectric constant.

[0020] Carborane has three isomers, p-carborane (FIG. 3), o-carborane(FIG. 4), and m-carborane (FIG. 5). Each isomer has two reactive C—Hbonds. These bonds can be synthetically modified by triethoxy (ormethoxy, propoxy, and butoxy) silanating agents or silinating agents tobecome depositable by chemical vapor deposition using triethylorthosilyl(TrEOS) or silyl (SiH3) functional carborane. In other words, byattaching TrEOS or silyl constituents, the carborane, which hasdesirable characteristics, may also be modified to be depositable bychemical vapor deposition.

[0021] TrEOS-carborane may be formed from a meta, ortho, or para isomerof carborane and a constituent of the form XSiR′₃ wherein X is a halogenor other reactive group, as shown in FIGS. 5 through 8 and R′₃ is analkyl such as a methoxy, ethoxy, propoxy or butoxy group. Similarly, ameta, ortho, or para carborane, together with a constituent of the formXSiH₃ may be reacted to form an SiH₃-carborane as shown in FIGS. 9through 12. Again, the X constituent may be a halogen.

[0022] The TrEOS-carborane and SiH3-carborane are chemical vapordepositionable molecular precursors. These precursors (shown, forexample, in FIGS. 1 through 12) can be deposited by themselves orco-deposited with SiOEt₄ (tetraethylorthosilicate; TEOS) or with SiH₄(silane) to form a three-dimensional carborane containing oxide filmshown in FIG. 13. Such a film may have a dielectric constant less than2.5 and strong mechanical structural properties due to the small cagestructure containing a three-dimensional network. The three-dimensionalstructure shown in FIG. 13, which is a three-dimensional structure, maybe formed as a result of the use of a carborane CVD precursor plus TEOSin a chemical vapor deposition or plasma enhanced chemical vapordeposition in accordance with one embodiment of the present invention.

[0023] As a result, a mechanically strong low dielectric material may bedeposited by chemical vapor deposition. The deposition can be done bychemical vapor deposition or plasma enhanced chemical vapor deposition(PECVD), leading to low dielectric constant carborane-deposited oxidethin films.

[0024] These thin films are stable since carborane is incorporatedchemically into the three-dimensional film. They have relatively lowdielectric constants because they are relatively non-polar and have lowcage densities. The film has a closed pore structure with a uniform poredensity of approximately one nanometer. The cage forms a relativelystrong film that is chemically bonded into the oxide network. No carbonor fluorine doping may be needed which normally leads to out gassing andthermal stability problems. Existing equipment infrastructure may beutilized to chemically vapor deposit these precursors.

[0025] The carborane may be attached to other moieties including analkyl moiety such as a methyl group (FIG. 1B) or a halogen such asfluorine or chlorine. Also, the carborane containing materials may bemixed with other dielectrics such as silicon dioxide, silicon nitride toreduce the dielectric constant of the composite material. Fluorinecontaining carboranes may have even lower dielectric constants (FIGS. 1Aand 1B).

[0026] While the present invention has been described with respect to alimited number of embodiments, those skilled in the art will appreciatenumerous modifications and variations therefrom. It is intended that theappended claims cover all such modifications and variations as fallwithin the true spirit and scope of this present invention.

What is claimed is:
 1. A semiconductor wafer comprising a film containing carborane and silicon.
 2. The wafer of claim 1 wherein the carborane is attached to an element including a constituent selected from the group including triethyl, methoxy, propoxy, butoxy, or orthosilyl group.
 3. The wafer of claim 1 wherein said carborane is attached to a silyl group.
 4. A method comprising: forming a film including carborane; and depositing said film on a semiconductor wafer using chemical vapor deposition.
 5. The method of claim 4 including forming the film with carborane and tetraethyl (or methyl, propyl, butyl) orthosilicate.
 6. The method of claim 4 including forming the film with carborane and silane.
 7. The method of claim 4 including depositing using plasma enhanced chemical vapor deposition.
 8. A dielectric film comprising: a caged molecular structure having a pore size less than two nanometers and a dielectric constant less than 2.5.
 9. The film of claim 8 wherein said caged molecular structure includes carborane.
 10. The film of claim 9 wherein said carborane is linked to a constituent selected from the group including tetraethyl, methyl, propyl, butyl, or orthosilicate.
 11. The film of claim 8 wherein said carborane is linked to silane.
 12. The film of claim 8 wherein said pore size is about one nanometer or less.
 13. A method comprising: forming a film having a pore size less than two nanometers and a dielectric constant less than 2.5; modifying said film to enable said film to be chemical vapor deposited by attaching a chemically vapored depositable material to said molecular structure.
 14. The method of claim 13 including forming a film including carborane.
 15. The method of claim 13 including attaching a constituent including a triethyl, methyl, propyl, butyl, or orthosilyl group to said molecular structure.
 16. The method of claim 13 including attaching silyl groups to said molecular structure.
 17. The method of claim 13 including forming a film with a pore size of about one nanometer or less. 